Refrigeration – Storage of solidified or liquified gas – Spraying of cryogen
Reexamination Certificate
2000-01-24
2001-12-04
Doerrler, William (Department: 3744)
Refrigeration
Storage of solidified or liquified gas
Spraying of cryogen
Reexamination Certificate
active
06324852
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method of and apparatus for cooling exothermic reactions in a reaction vessel with a highly pressurized liquid cryogen.
BACKGROUND OF THE INVENTION
Cryogenic liquids may be used to cool exothermic reactions due to their refrigeration properties. A particularly direct approach would be to inject the liquid cryogen directly into the liquid reactants within a reaction vessel, thereby eliminating the potential freezing and fouling of the heat transfer surfaces. The liquid cryogen vaporizes instantaneously upon contacting the reaction mixture and transfers both the latent heat and the sensible heat to its surroundings.
However, injecting the liquid cryogen directly into the reaction vessel has proven very difficult because the liquid cryogen storage tank may be optimized only for a given pressure. For reaction tanks which are withdrawing both a liquid cryogen for cooling and a gas for blanketing, purging and other applications, for example, liquid nitrogen and nitrogen gas, it is necessary to set the tanks at the high working pressure. Therefore, the liquid cryogen must be withdrawn also at high pressure, e.g., 150 psi, but such an operating pressure is unfavorable for most liquid cryogen applications.
The problem with supplying liquid cryogen at high pressures is that the liquid cryogen will be saturated with the gaseous phase of the cryogen. When the pressure is reduced due to frictional losses, e.g., from valves or elevation, the liquid cryogen will flash off from the liquid as a gas. Since the gas may occupy several hundred times the volume of the liquid cryogen, gas will create blockage to the liquid cryogen line resulting in a substantial pressure drop and reduction in liquid cryogen supply. A reduction in the liquid cryogen supply may be a potential safety hazard when the cooling capacity is lost during the peak of self-accelerating exothermic reactions.
Conventional cryogenic cooling systems keep the supply pressure from the liquid cryogen storage tank low, e.g., about 50 psi, to minimize flashing across the valves. When there is a need for high pressure gas for blanketing, purging, etc., two separate tanks are required. For example, high pressure liquid nitrogen is transferred from trucks or the high pressure liquid nitrogen storage tank into a low pressure liquid nitrogen storage tank. The gas saturated at higher storage pressure will be venting off in the gas phase as it enters the low pressure storage tank. The vented gas is a lost product. Furthermore, flashing occurs when the liquid cryogen flows across any restricted devices such as pressure regulators or control valves. Unfortunately, these devices are necessary for precise temperature control of the reaction processes. Flashing across a control valve may cause the flow to stop due to vapor lock. Thus, it would be desirable to eliminate the need to transfer the liquid cryogen from a high pressure tank to a low pressure tank thereby reducing the lost of the vented gas. Also, it would be desirable to provide a liquid cryogen cooling system wherein flashing of the liquid cryogen is eliminated or substantially reduced.
Another conventional approach uses a sub-cooler wherein a portion of the liquid cryogen such as liquid nitrogen is diverted into a separate chamber and boiled off at reduced atmospheric pressure. The boiling liquid is heat exchanged with the main stream of liquid nitrogen at the higher pressure. Since the boiling point of the liquid nitrogen is lower at reduced pressure than the liquid nitrogen at the higher pressure, the boiling liquid nitrogen is capable of sub-cooling the liquid nitrogen at the lower pressure and condenses the nitrogen gas bubbles back into liquid. The vaporized nitrogen at the lower pressure is discharged to the atmosphere because it loses its pressure head and latent heat refrigeration value. The amount of loss will increase with the pressure of the liquid nitrogen storage tank, room temperature and frictional loss of the liquid nitrogen supply. Although the sub-cooled liquid nitrogen will have less tendency to flash off across the valves and fittings since the temperature is below its boiling point, additional liquid nitrogen must be diverted to the sub-cooler in order to provide sufficient refrigeration to sub-cool or condense the gas as the refrigeration quality of the liquid nitrogen supply is decreased. Thus, it would be desirable to eliminate the need to sub-cool the liquid nitrogen while retaining the refrigeration quality of the liquid nitrogen supply.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method of and apparatus for supplying liquid cryogen at high pressure with minimal flashing.
It is another object of the present invention to provide a method and apparatus for supplying liquid cryogen at high pressure directly into a reaction vessel for optimal cooling of exothermic reactions.
A further object of the invention is to eliminate the need to sub-cool the liquid cryogen while retaining the refrigeration quality of the liquid cryogen supply.
It is yet another object of the present invention to provide a single source for both high pressure gaseous nitrogen and high quality liquid nitrogen.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
SUMMARY OF THE INVENTION
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in a first aspect, a liquid cryogen delivery system comprising an injector tube having a first end and a second end, a liquid cryogen source for supplying a flow of liquid cryogen into the injector tube, and a drive shaft within the injector tube, the drive shaft being movable towards the first end of the injector tube to discontinue the flow of liquid cryogen from the first end of the injector tube.
Preferably, the liquid cryogen delivery system further includes a shielding gas source for continuously supplying a shielding gas through the first end of the injector tube independent of the flow of liquid cryogen into the injector tube. Furthermore, a nozzle may be attached to the first end of the injector tube wherein the shielding gas forms a gas pocket adjacent a nozzle end to prevent reactants from freezing and clogging the nozzle when the liquid cryogen delivery system is used in conjunction with a reaction vessel.
In another aspect, the present invention is directed to an apparatus mounted into a reaction vessel for cooling a reaction within the vessel with a high pressure liquid cryogen comprising an injector tube having an inner concentric tube and an outer concentric tube having outlets at a first end of the injector tube, and a sealed second end, a drive shaft positioned within the inner concentric tube, a means for moving the drive shaft to regulate the outlet of the inner concentric tube, and a liquid cryogen supply connected to the inner concentric tube.
Preferably, the drive shaft has a plug adapted to fit into the outlet of the inner concentric tube to seal off the inner concentric tube. Preferably, the means for moving the drive shaft to regulate the outlet of the inner concentric tube comprises a manual drive mechanism to linearly move the drive shaft, a mechanical drive mechanism to linearly move the drive shaft, or a linear motor. Preferably, the liquid cryogen supply is selected from the group consisting of nitrogen, hydrogen, oxygen, helium, carbon dioxide, air and combinations thereof having a maximum pressure of about 3000 psi. Most preferably, the liquid cryogen supply comprises liquid nitrogen at a pressure of about 30 psi to about 300 psi.
This aspect may further include a shielding gas supply connected to the outer concentric tube adapted to provide a continuous flow of a shielding gas to prevent the liquid cryogen from freezing the nozzle and reactants in the vessel. Preferably, the shielding gas supply has a lower temperature
Doerrler William
Lau Bernard
Praxair Technology Inc.
LandOfFree
Method of using high pressure LN2 for cooling reactors does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of using high pressure LN2 for cooling reactors, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of using high pressure LN2 for cooling reactors will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2599450